In the area of conventional xerography and photocopying, an image is generated according to reflected light from an original image. Referring to FIG. 1, a light source 20 emits light towards an original image 105 (hereinafter "an original") placed on a platen glass 110. The light transmits through the platen glass 110 and reaches the original 105, and the original reflects the light back towards the light source 20. The reflected light is then converted to a electronic signal so as to generate a corresponding image via toner placed on a photoreceptor 22. In a certain image conversion process, an electronic device such as a CCD is used before generating a photoreceptor image. In certain other image processing, the photoreceptor image is generated via the direct optical means such as mirrors and lenses. In either case, in order to accurately reflect the original image by reflecting the light emitted from the light source, the original must have a substantially smooth surface. However, the light reflecting surface of the original is not always smooth.
As shown in FIG. 2, an additional original 106 is placed on the surface of the original 105. For example, the additional original portion 106 may be a photograph pasted on an application. Because of the additional width of the attached portion 106, areas 107 adjacent to the edges of the attached portion 106 are shadowed. In other words, in this example, since the light emitted from the light source is not perfectly perpendicular to the edges of the attached portion 106, the edges of the attached portion prevents the light from reaching the areas 107 adjacent to the edges of the attached portion 106. Consequently, since the shadowed area 107 is duplicated as a dark area, a copy has undesirable dark edges around the attached portion 106. Similarly, even if no attachment is placed on the original, an uneven or wrinkled original causes a similar shadowing effect.
To prevent the above described undesirable shadow effect caused by the uneven surface of the original, prior attempts included various approaches. Earlier approaches included a plurality of flash lamps for emitting light in diffused directions. However, this approach required a larger housing to accommodate the plurality of these lamps. A second group of approaches included a light diffusing element which is placed between a platen glass and an original to solve the above described shadow problem.
Referring to FIGS. 3A and 3B, the original 105 and the attached portion 106 are placed on the top of a light diffusing element 120 with the attached portion 106 directly contacting the light diffusing element 120. The above described assembly of the original 105, the added portion 106 and the light diffusing element 120 is placed on the platen glass 110 with the light diffusing element 120 contacting the platen glass 110. As shown in a cross sectional view in FIG. 3B, when a copy is made from the above described original, the light emitted from the copier light source 20 reaches the platen glass 110 and then the light diffusing element 120 before reaching the original 105 or the added portion 106.
The light diffusing element 120 diffuses light as it transmits through the layers. Referring to FIG. 4A, a principle as to how the element 120 diffuses the emitted light is diagrammatically illustrated in a cross sectional view. Since the element 120 has certain refracting layers or a rough surface, certain light is reflected in an angle on an outer surface B while certain other light is reflected on an inner surface C at an angle. Yet, other light is refracted as it transits through the element 120. Consequently, the light reaching the original or added portion surfaces is diffused. As shown in FIG. 4B, the light diffused by the element 120 now reaches areas 107 around the edges of the added portion 106 to substantially eliminate the shadow areas.
Based upon the above described solution, Japanese Utility Model Application No. 61-79326 utilized a platen glass whose surface has fine peaks and valleys for diffusing light before reaching an original. Although the above platen glass reduced the shadow effect, the rough surface undesirably trapped dust and the dirty platen glass consequently deteriorated the copy image quality. The costs and the efforts associated with maintaining or replacing a dust-free platen glass were prohibitive.
In the alternative, Japanese Patent No. 60-260942 discloses a light diffusing sheet placed over a platen glass so that light is diffused before reaching a metal surface to be photocopied. Although light may be diffused for solving the above described shadow problem, the above Japanese patent discloses only a manual mode of the duplication process. In contrast to this disclosure, most photocopiers today are equipped with an automatic document feeder to facilitate the duplication of multiple pages. Some automatic document feeders are capable of duplicating two sides of an original. The use of the light diffusing sheet in an automatic document feeder. An automatic document feeder should be able to accommodate the additional thickness of the above described carrier sheet.
In addition, the above described light diffusing element placed on an original generally modifies the duplication process. For example, since a light source is calibrated to emit an appropriate amount of light to reach an original through a platen glass, the light source intensity must be adjusted to accommodate the light diffusion caused by the above described light diffusing element or a carrier sheet. The user should be able to use the light diffusing material without manually adjusting any processing characteristics. These and other features remain to be desired.